Trends in perinatal mortality were studied in the city of Pelotas, Southern Brazil, using three population-based cohort studies carried out in 1982, 1993 and 2004. The objective of the present study was to analyze trends and differences in perinatal mortality during the 1982-2004 period. All hospital deliveries and perinatal deaths were monitored through daily visits to maternity wards. Cause of death was determined using information from hospital records and by interviewing physicians. Perinatal mortality fell by 43% in the two decades, with a greater reduction between 1982 and 1993. Intrapartum fetal deaths decreased by 72% and deaths from asphyxia fell from 4.5 per thousand in 1982 to 1.4 per thousand in 2004. In conclusion, reductions in perinatal mortality were also seen across all birth weight categories between 1982 and 1993, but the same was not true for the 1993 to 2004 period, when mortality increased in several categories above 2,000g.